//Write a program to find the node at which the intersection of two singly linke
//d lists begins. 
//
// For example, the following two linked lists: 
//
//
// begin to intersect at node c1. 
//
// 
//
// Example 1: 
//
//
// 
//Input: intersectVal = 8, listA = [4,1,8,4,5], listB = [5,0,1,8,4,5], skipA = 2
//, skipB = 3
//Output: Reference of the node with value = 8
//Input Explanation: The intersected node's value is 8 (note that this must not 
//be 0 if the two lists intersect). From the head of A, it reads as [4,1,8,4,5]. F
//rom the head of B, it reads as [5,0,1,8,4,5]. There are 2 nodes before the inter
//sected node in A; There are 3 nodes before the intersected node in B. 
//
// 
//
// Example 2: 
//
//
// 
//Input: intersectVal = 2, listA = [0,9,1,2,4], listB = [3,2,4], skipA = 3, skip
//B = 1
//Output: Reference of the node with value = 2
//Input Explanation: The intersected node's value is 2 (note that this must not 
//be 0 if the two lists intersect). From the head of A, it reads as [0,9,1,2,4]. F
//rom the head of B, it reads as [3,2,4]. There are 3 nodes before the intersected
// node in A; There are 1 node before the intersected node in B.
// 
//
// 
//
// Example 3: 
//
//
// 
//Input: intersectVal = 0, listA = [2,6,4], listB = [1,5], skipA = 3, skipB = 2
//Output: null
//Input Explanation: From the head of A, it reads as [2,6,4]. From the head of B
//, it reads as [1,5]. Since the two lists do not intersect, intersectVal must be 
//0, while skipA and skipB can be arbitrary values.
//Explanation: The two lists do not intersect, so return null.
// 
//
// 
//
// Notes: 
//
// 
// If the two linked lists have no intersection at all, return null. 
// The linked lists must retain their original structure after the function retu
//rns. 
// You may assume there are no cycles anywhere in the entire linked structure. 
// Your code should preferably run in O(n) time and use only O(1) memory. 
// 
// Related Topics 链表
// 双指针 解法


//leetcode submit region begin(Prohibit modification and deletion)
/**
 * Example:
 * var li = ListNode(5)
 * var v = li.`val`
 * Definition for singly-linked list.
 * class ListNode(var `val`: Int) {
 *     var next: ListNode? = null
 * }
 */

class Solution {
    fun getIntersectionNode(headA:ListNode?, headB:ListNode?):ListNode? {
        if (headA == null || headB == null) {
            return null
        }
        var pA = headA
        var pB = headB
        while (pA != pB) {
            if (pA?.next == null && pB?.next == null) {
                return null
            }
            pA = pA?.next ?: headB
            pB = pB?.next ?: headA
        }
        return pA
        
    }
}
//leetcode submit region end(Prohibit modification and deletion)

/** 暴力
fun getIntersectionNode(headA:ListNode?, headB:ListNode?):ListNode? {
var p = headA
while (p != null) {
var q = headB
while (q != null) {
if (p == q) {
return p
}
q = q.next
}
p = p.next
}
return null

}
 */
